The invention relates to an antenna for transmitting and receiving signals.
Helical antenna elements for antennas for telecommunications devices are known, for example from Published, Non-Prosecuted German Patent Application DE 196 39 642 A1, which discloses a retractable antenna device having a helical antenna section.
Published, Non-Prosecuted German Patent Application DE 42 05 084 A1 discloses a pair of conductor structures for receiving electromagnetic waves, in which each element of the pair is constructed to form an overall structure including individual elements. The individual elements are connected to one another in series and are stacked in planes one above the other. Each pair of individual elements in each plane is configured such that the turns of the spiral run in opposite directions to one another. The individual elements in each plane are in the form of spiral, planar structures. The above-mentioned documents do not deal with any measures to reduce the possibility of the antennas being slightly mistuned by capacitive influences from the environment or to increase the bandwidth of the antennas in comparison to an individual antenna.
One possible way to reduce capacitive influences with the aid of a radio-frequency counterpoise is described in the document by Haapala P. et al., xe2x80x9cDual Frequency Helical Antennas for Handsetsxe2x80x9d, IEEE Vehicular Technology Conference, US, New York, IEEE, Conf. Proc. 46, pages 336-338, XP000594306, in which case the radio-frequency counterpoise results in an increase in the base impedance of the antenna. This document also describes a parallel circuit formed by two antenna elements having helical sections but, in this case, the bandwidth of one of the two antenna elements is reduced in comparison to that of a single antenna.
It is accordingly an object of the invention to provide an antenna for transmitting and receiving signals which overcomes the above-mentioned disadvantages of the heretofore-known antennas of this general type and which allows a wider bandwidth and better matching to a radio-frequency counterpoise and to a feed line system.
With the foregoing and other objects in view there is provided, in accordance with the invention, an antenna for transmitting and receiving signals, including
at least a first antenna element and a second antenna element for transmitting and/or receiving signals of a same frequency;
the at least first and second antenna elements having a helical shape and being disposed parallel to one another;
a common conductor surface, the at least first and second antenna elements being individually connected in parallel to the common conductor surface; and
a radio-frequency counterpoise, the at least first and second antenna elements being capacitively coupled to the radio-frequency counterpoise via the common conductor surface.
In other words, the object of the invention is achieved by an antenna for transmitting and receiving signals having at least a first and a second antenna element for transmitting and receiving signals at the same frequency, with the antenna elements having a helical or spiral shape, being provided parallel to one another, in each case being connected individually to a common conductor surface and connected in parallel, and being capacitively coupled to a radio-frequency counterpoise via the conductor surface.
Due to their compact structure, such antennas can be used as internal antennas in telecommunications apparatuses, such as cordless telephones.
The two or more antenna elements which are provided parallel result in a wider bandwidth, as a consequence of which the antenna according to the invention is less sensitive to capacitive influences from the environment. Furthermore, higher currents which are induced at the base point or feed point of the antenna and are better distributed over a large area allow the two or more antenna elements to be better matched to the radio-frequency counterpoise and to the feed line system.
The antenna elements are preferably coupled to the radio-frequency counterpoise through the use of a capacitive coupling element. The capacitive coupling element may in this case include conductor surfaces which are printed on opposite sides of the radio-frequency counterpoise.
According to another feature of the invention, the at least first and second antenna elements are coupled to the radio-frequency counterpoise with a capacitive coupling element.
According to yet another feature of the invention, the radio-frequency counterpoise has opposite sides and the capacitive coupling element is a printed structure provided on the opposite sides.
According to a further feature of the invention, the at least first and second antenna elements include helical coils.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an antenna having a wide bandwidth, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.